I want to thank the thousands of folks here for giving me the inspiration to get my 1949 Ford and build it up. What a wonderful community! I come to y'all in all humility to make sure I am not overlooking something. Car drives great but the high idle is driving me nuts. Here are steps I have taken (I will try to keep organized to not waste your time) PROBLEM: High idle 1100-1200 in park (900 in gear) ENGINE: 302 mild cam/ mild heads/ summit intake/ edelbrock performer 600cfm (new carb) Fuel pump: electric "helper" near tank and mech on motor Fuel filter: came with carb Gas: brand new no ethanol Timing: 10-14 degrees base with vacuum unhooked (no change in idle until under 6 or over about 16) AFR: Air fuel meter shows little or no change in idle RPM between 12 and about 15 when I adjust the idle mix screws (I installed this 9" past the driver header collector) The following interventions have been undertaken: VACUUM LEAK IDENTIFIED with starter fluid driver intake edge and carb base new carb base gasket--no change Pulled manifold and placed new gasket/ gaskacinch/grey GM on water ports/right stuff on intake ends--fixed vacuum leak but no change in RPM VACUUM HOSES confirmed that plugging all vacuum lines from carb had no effect on idle. 20" of vacuum at idle. IDLE LINKAGE SCREW all the way out CHOKE confirmed that choke is operating correctly (electric choke opens fairy soon after key on) FAST IDLE CAM: confirmed that RPM drops when I bump throttle so it is not staying on the fast idle cam MANIFOLD inspected, no cracks...I did note that carb spacer was rectangular and not the "4 hole" type but I do have that type and gaskets if I need to change--thoughts? CARB I don't see anything visibly wrong with the carb, the motor dies quickly if I cover it with a rag NON-IDLE PERFORMANCE Great acceleration/ lights the tires up/ AFR reads 13.5 throughout the rpm range In closing, the readings and behavior makes me think it is simply allowing too much of a pretty good air fuel mix in. But how exactly can I tell how much air is going through....is this just a test by looking at the butterflies with the carb off the motor or is there more too it? All help appreciated. Please feel free to point out anything I have done wrong I am here to learn.
Confirm that all four butterflies are solidly closed when idle screw is backed out. You may have a bent carb linkage that is allowing one or more butterflies to remain partially open. Even though the carb is new doesn't mean that it was never dropped. Good luck!
Throttle return spring pulling butterflies closed? Throttle linkage allowing butterflies to close fully?
Carefully check the gasket between the intake and carb. Often there is an area that is not covered by the gasket or spacer. You can often see the imprint of this on the gasket. Also the gasket can catch the butterfly and keep it open a tiny bit.
Just because the RPM drops when you blip the throttle doesn't mean you are totally off the fast idle cam. Have you looked at it to be sure? It could still be on the last step of the FI cam.
I am running a 1406 on a SBC. I found that over the counter carb mounting gaskets did not properly "fit" the carb base and left a small gap. Double check your mounting gasket that it properly seals on the manifold and carb.
BJR thank you Sir I will doublecheck. This is a great point. Missydad and Anothercarguy I am going to admit that I overlooked something. After shimmying up over the high idling motor it appears that the front butterfly valves are open in a crescent with the maximum gap (thickest part of the moon) being about 1/16 of an inch. The moon opening is in the normal opening direction of the carb, and opening the carb even a tiny bit (as small as my eye can detect) picks up 200-300 rpm (estimated) so it appears to be a pretty significant amount of air/fuel getting in. It likewise appears that it doesn't take much to raise the rpm from a low to a high idle. I will check the fast idle cam as suggested. Is there any way to "index" the primary butterfly valves to the linkage, such that it is closed when the linkage is closed? It appears that the actual rotating shaft is connected to these. Is the arm splined so that I could rotate it slightly? It seems obvious that they are not closing I think I did not look closely enough initially.
Yes Sir I did it feeds power brakes and vacuum wipers 1/4 npt with thread sealant but I tested with this plugged just to be sure that nothing was leaking.
Guys I solved it with your help. There is a tiny gold screw below the idle speed screw, it cracks open the butterfly valves and was tightened way down. I loosened it and the idle fell, tweaked the adjustment screws and got the AFR 13.5-14. Thank you for all the help. I am red with embarrassment but green with experience!
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